This invention relates to method and apparatus for feed through connections.
More particularly, this invention relates to feed through devices for supply lines or utility carriers such as a cable, a wire or a pipe, which must be passed through an aperture in a structure such as a wall of a building, the casing of a machine or a locating device in electrical apparatus.
When supply lines, especially flexible supply lines, are fed through an aperture, it is important that the danger of rupture of the supply line caused by the rough edges of the aperture be minimized. It is also generally necessary that the supply lines be firmly held in relation to the aperture to avoid unwanted movement of the supply line both within the aperture itself and on either side of it. FInally, it is important, especially when the supply line passes from an external location to an internal location, that the feed through connection utilized be firmly sealed against the ingress of moisture and other contaminants such as small insects.
In the past, various feed through devices have been proposed for such purposes including flexible grommets, usually made from rubber or a similar material. These grommets were provided with two terminal shoulders which located the grommet firmly within the aperture. The overall outer diameter of the grommet is slightly larger than that ofthe aperture into which it is placed to ensure a tight fit, and the inner diameter of the grommet is slightly less than that of the supply line which is passed through it to ensure that the latter is firmly gripped by frictional and resilient forces. Such grommets have proved suitable for general applications such as with electrical apparatus since they adequately protect the supply line, e.g., a wire or cable, against the sharp edges of the apertures which are stamped or bored in associated metal panels.
However, these grommets generally suffer from the disadvantage that they can only be used over a small range of tolerance regarding the size of the aperture and the size of the supply line. Furthermore, they are generally not satisfactory for larger scale uses especially in outdoor/indoor applications where protection against moisture, etc., is of paramount importance.
The present invention lessens the prior art difficulties by providing a method of feeding a supply line through an aperture and firmly locating the supply line within the aperture. This is accomplished by positioning a hollow heat recoverable member or article around the supply line and at least partially within the aperture, the heat recoverable article being constructed of two or more portions or parts. A first portion or part is heat shrinkable and a second is heat expansible. Heating of the heat recoverable article results in the shrinkage of the heat shrinkable part to firmly grip the supply line. The heating also results in the heat expansible part expanding and firmly locates the heat recovered article, and thereby the supply line, within the aperture.
The present invention also provides a generally tubular heat recoverable article suitable for use in the method of the present invention.
The heat recoverable article may take various forms, depending on the particular application concerned. For example, in some cases it may be sufficient that a heat shrinkable part is provided at only one end of the article (i.e., so that it operates only on one side of the aperture), but in other cases it may be desirable to provide a heat shrinkable part at both ends in order to strengthen and give increased firmness to the feed through connection. In this latter case the heat recoverable article may comprise, for example, a central heat expansible part and two heat shrinkable end parts.
However, in a preferred embodiment of the present invention, the article comprises an outer heat shrinkable tube which surrounds, and overlaps at each end, an inner heat expansible tube. The strength of recovery of the latter being the greater so that, when the article is completely recovered, the central portion of the article expands and locates the article within the aperture and the two overlapping heat shrinkable end portions shrink down and grip the supply line.
The heat expansible and heat shrinkable parts of the articles of the present invention may be held together by the use of adhesives, but, in more cases, it will be preferable to form the articles by partially heat shrinking the heat shrinkable part(s) so that it comes into contact with and firmly grips the heat expansible part(s). An ahdesive may also be used in this latter case, such as a hot melt adhesive.
Adhesives may also be used to improve the strength of the feed through connection. For example, the heat shrinkable part(s) may be provided with an inner lining of an adhesive and/or the heat expansible part(s) may be provided with an outer layer of an adhesive. Alternatively, the adhesive may be applied separately when making the connection. Especially suitable, are hot-melt adhesives such, for example, as polyamide-type materials, ethylene/vinyl acetate copolymers and terpolymers (with or without incorporated paraffin waxes) and polyesters. these can be provided as an inner or outer lining, respectively, on the heat recoverable parts and melt and flow on recovery of the latter to form the desired bond and seal. Also suitable are semi-hot melt adhesives such as polyethylene based materials including peroxide curing agents which will also melt and flow on recovery, but which will not afterwards be hot-meltable in view of the action of the curing system. Amongst suitable adhesives which can be applied to the portions during the making of the feed through connection there may be mentioned, for example, eppoxy resins and conventional mastics such as, for example, those based on butyl and natural rubbers with incorporated pitch and similar materials. Obviously the type of adhesive employed and the method of its application will depend on the particular requirements in any given case.
Any heat recoverable material may, in principle, be used in the present invention although the most suitable material will usually depend on the environment in which the connection is being made. Suitable materials are disclosed, for example, in U.S. Pat. No. 3,297,819, assigned to the assignee of the present invention, the disclosure of which is incorporated herein by reference. Examples of such suitable materials are cross-linked polyolefines, especially polyethylene, cross-linked polyvinylidene fluoride, such as that sold under the trademark Kynar, cross-linked polyvinyl chloride, normal (unmodified) polyvinyl chloride, cross-linked or uncross-linked chlorinated polyethylenes, neoprene, ethylene propylene rubbers and silicon rubbers. Cross-linked Kynar is especially preferred for use in the present invention.
The method and article of the present invention facilitate a rapid and strong feed through connection while considerably reducing the strain at the aperture. The supply line is "loosely" located in the aperture because of the relative flexibility of the heat recoverable article itself, especially the heat expansible portion thereof, and any bending, twisting or other strains at the entrance to or exit from the aperture are largely accommodated by the heat recoverable article.
The dimensions of the heat recoverable article and degree of shrinkage and expansion will be chosen such that the fully shrunk dimension of the shrinkable portion(s) is less than the corresponding outer dimension of the supply line and such that the fully expanded dimension of the expansible portion is greater than the corresponding dimension of the aperture. However, subject to these provisions it will be obvious to one skilled in the art that because of the large potential degree of expansion and shrinkage, respectively, available in the heat recoverable article, the latter can be used over a wide range of dimensional tolerances both with regard to the size of the aperture and the size of the supply line. This is another outstanding advantage of the present invention.